The present invention relates to an ink jet recording apparatus and an ink jet recording method in which images are formed by ejecting, from an ink jet recording head, an ultraviolet radiation curable ink which is capable of undergoing reaction and being cured by exposure to ultraviolet radiation and subsequently fixed, and more specifically to an ink jet recording apparatus as well as an ink jet recording method in which, even though images are formed employing a plurality of recording modes which differ in image recording rate, high quality images are always formed.
In recent years, section to form color images on various recording materials have been markedly diversified, and images are produced employing diversified section such as conventional silver salt photography which has been widely employed to, for example, color paper, as well as electrophotographic systems and ink jet recording systems.
Particularly, since ink jet recording systems are capable of simply preparing images at low cost, this is applied to various printing fields such as photography, various kinds of printing, or specialized printing such as marking or color filters. Specifically, by employing combinations of an ink jet recording system apparatus (an ink jet printer) which ejects and controls minute dots, an ink which exhibits improved color reproduction range, durability, and ejection adaptability, and special paper which exhibits markedly improved ink absorbability, color forming properties of colorants, and surface gloss, it is possible to achieve image quality comparable to silver salt photography. Current improvement of image quality obtained by the ink jet recording system is finally achieved by the integration of the ink jet printer, and ink and special paper employed in the aforesaid ink jet printers.
However, in ink jet printers which require special paper, recording media are limited. As a result, cost of recording media increases and the application field of the ink jet printers is limited. Consequently, many trials have been conducted in which recording is achieved on recording media different from special paper sheets, employing an ink jet system. Specifically, included are a phase variation ink jet system employing a wax ink which is solid at room temperature, a solvent based ink jet system which uses ink comprised of quick drying organic solvents as a main component, and a UV ink jet system in which after recording, crosslinking is achieved employing ultraviolet (UV) radiation.
Of these, in recent years, UV ink jet systems have received specific attention due to relatively low generation of unpleasant odor compared to solvent based ink jet systems, rapid drying, and capability of recording on non-ink absorptive recording media. For example, Japanese Patent Publication No. 5-54667, and Japanese Patent Publication Open to Public Inspection Nos. 6-200204 and 2000-504778 disclose ultraviolet radiation curable ink jet inks.
Ultraviolet radiation curable inks are divided mainly into solvent-free ultraviolet radiation curable inks comprising minimal non-curable solvents and water based ultraviolet radiation curable inks in which photopolymerizable compounds are dissolved or dispersed into water based media.
Since it is possible to cure the solvent-free ultraviolet radiation curable ink only by exposure to ultraviolet radiation and then to dry the resultant image, it exhibits advantages such as suitability for high speed image recording and minimal generation of hazardous substances such as VOC (volatile organic compounds). As a result, it has been put into practical use. However, the solvent-free ultraviolet radiation curable ink results in no volume contraction during curing. As a result, deposited ink droplets result in tactile roughness and also a feel of quality different from common printed matter.
However, it is possible to minimize the aforesaid tactile roughness in such a manner that exposure to ultraviolet radiation is delayed to a degree in which bleeding results in minimal problems so that ink droplets result in leveling. Simultaneously, it is possible to improve color reproduction. Namely, in order to control the characteristics of formed images, a method is effective in which duration from ink ejection to exposure to ultraviolet radiation and radiation intensity are controlled to optimal conditions.
Disclosed as one of the aforesaid methods (for example, refer to Patent Document 1 as well as Non-Patent Document 1) is a method in which wettability of ink which is further deposited on the former ink is improved by limiting the energy of exposed ultraviolet radiation of the primary exposure to 5 percent.
However, according to investigations performed by the inventors of the present invention, when image recording is carried out employing an ink jet printer having a plurality of recording modes which differ in image recording rate, no desired results are obtained by only simply controlling the initial exposure energy.
Specific descriptions will now be made.
Referring to FIG. 1, an example is described in which images are formed employing a serial printing system while ultraviolet radiation sources for exposure are installed at both ends of a carriage fitted with an ink jet recording head.
As shown in FIG. 1, two-way printing is carried out employing the serial printing system. When an ink jet image is formed employing 4 passes in total (two reciprocating motions), the cases described below occur as the state of the position on which ink is deposited onto a recording material at the fourth final pass.    1) The surface of the recording material remains as it is and an ink surface on which no printing is carried out    2) An image formed by other ink ejected in the same scanning and an ink surface which is not yet exposed to ultraviolet radiation    3) An ink surface comprising an image which has been twice exposed to ultraviolet radiation    4) An ink surface comprising an image which has been exposed to ultraviolet radiation four times    5) An ink surface comprising an image which has been exposed to ultraviolet radiation six times
In addition, various images under different situations exist in the state in which each cases 2)–5) overlap. Further, in images which have been subjected to the fourth pass printing and exposure to ultraviolet radiation employing the aforesaid method, images are formed while mixed with ink printing portions which have been subjected to various frequency of exposure to ultraviolet radiation such as 1–7.
In the foregoing, description was made referring to the example in which ink jet images are formed employing two-way printing under 4 passes (two reciprocating motions). However, in practice, desired resolution, the printing method (two-way or one-way printing), or the frequency of passes differs. As a result, the number of cases corresponding to each differs. For example, in one-way printing, when images are formed under interleave of 3 and 12 passes, various ink images which have been exposed to ultraviolet radiation of the frequency of 0–19 simultaneously exist on the recording material at ink deposition.
Further, when taking into account combinations of a plurality of colors, the number of the resulting cases markedly increases. As a result, it is impossible to control each of them to be optimal conditions.
Generally, the diameter of deposited ink droplets depends on either recording materials used as a substrate or the history of exposure of ultraviolet radiation to ink. In conventionally disclosed case examples, no description is made with regard to how optimal conditions are set employing what type of ink having any history of exposure to ultraviolet radiation is used as a standard.
(Patent Document 1)
Specification of U.S. Pat. No. 6,457,823
(Non-Patent Document 1)
Industrial Application of UV-Curing Jet Ink, Niegel Caiger, DDP2001 Final Program and Proceedings, 161